Connecticut and California State Tax - Income from Other States

[Yujin-Bao]

I'm a Connecticut (CT) resident for CT state tax purposes. In 2025 I had an internship in California for 3 months. I wonder if I need to file the income I received during my internship to both Connecticut and California for CT tax? If I understand the regulations correctly, I'm considered as CT resident and CA nonresident and need to include my CA income in all my earnings for CT tax, but only need to file CA income for CA tax. Please correct me if I'm wrong, and I would be grateful for any information on that!

[MaryK4]

You are correct- as a Connecticut resident, you must file a resident return reporting all income (including the CA internship) and a California non-resident return reporting only the income earned in CA. You will receive a credit in CT for taxes paid to CA to avoid double taxation. 

In TurboTax, you will want to file your California nonresident return first, then the Connecticut resident return so that the  credit for the taxes paid to California can be applied correctly.

[Yujin-Bao]

Thanks very much for the reply! May I ask how the CT credit works in this case? Is it a refund from CT for the tax I need to pay to CA and can it be deposited directly to my bank account or applied back to CT tax return as a 'deduction' (similar to property tax)?

[MaryK4]

Essentially, TurboTax calculates the amount of tax you paid to California on the same income taxed in California and applies it like a payment toward the taxes so you do not pay tax twice.  It requires calculation because you have to determine the tax that California applied to the income and the amount Connecticut applied.  

So, as an example, if the California income is $10,000 and you paid $500 of tax to California but Connecticut tax on the same $10,000 is $450, your credit is $450 (it zeros out the double tax).  If California’s tax rate is higher than Connecticut’s, you will only receive credit up to the amount Connecticut would have taxed you; you will not get a refund from Connecticut for the "extra" tax paid to California. 

@Yujin-Bao 

[Yujin-Bao]

Thanks so much for the detailed explanation! However, I'm now a bit confused about the CT regulations. I'm an international student on an F1 visa. I stayed in my leased place for more than 183 days in CT in 2025. From the CT regulations (https://portal.ct.gov/drs/individuals/nonresident-part-year/tax-information#whomustfile), I am a resident for 2025 if:

 - Connecticut was my domicile (permanent legal residence) for the entire 2025 taxable year, or

 - I was not domiciled in Connecticut, but you maintained a permanent place of abode in Connecticutduring the entire 2025 taxable year and spent a total of more than 183 days in Connecticut during the2025 taxable year.

They also define the permanant place of abode by: a residence (a building or structure where a person can live) that youpermanently maintain, whether or not you own it, and generall includes a residence owned by or leased toyour spouse. A place of abode is not permanent if it is maintained only during a temporary stay for the accomplishment of a particular purpose.

I did lease it and legally stayed there, but I can also interpret it as 'I'm living in CT for accomplishment of my study'. So I technically should be regarded as CT nonresident, even if I'm already a resident alien for federal tax purposes?

[DaveF1006]

Based on your situation and the Connecticut (CT) Department of Revenue Services (DRS) guidelines you cited, here is a breakdown of how to determine your status and how the "Credit for Taxes Paid to Another Jurisdiction" works.

 Connecticut defines a Resident in two ways. You only need to meet one of these to be considered a resident:

1. The Domicile Test: Connecticut is your "true, fixed, and permanent home." Since you are an international student on an F-1 visa, your domicile is generally considered your home country, as you typically intend to return there.
2. The Statutory Resident Test: You are a resident if you maintain a "permanent place of abode" in CT for the entire year AND spend more than 183 days in the state. This pertains to you in this case.

You mentioned the rule that a place is not permanent if it is for a "temporary stay for the accomplishment of a particular purpose" (like a degree).

1. In practice, CT tax authorities often view a year-long apartment lease as a "permanent place of abode" even for students. However, if your stay in CT is strictly limited to the duration of your studies and you maintain no other ties, you may have a case for being a Nonresident. 
2. If you determine you are a Nonresident, you only pay CT tax on income earned inside CT. If you determine you are a Resident, you pay CT tax on your worldwide income (including the CA internship), but you get a credit for the tax paid to CA.

If you file as a CT Resident, you will indeed be "double taxed" initially, but the Credit for Income Taxes Paid to Another Jurisdiction (Schedule 2 of Form CT-1040) fixes this. The credit is the lesser of:

1. The tax you actually paid to California.
2. The amount of CT tax attributable to that California income.

What this means is that if you earned $10,000 in California.

1. California Tax: CA has high tax rates. Let’s say they charge you $500. 
2. Connecticut Tax: CT has a lower rate for that bracket. Let’s say they charge you $450 on that same $10,000.
3. The Credit: CT will give you a credit of $450. This completely wipes out the CT tax on that income. You do not get the extra $50 back from CT; you simply "lose" that $50 to California.

If you file as a  CT resident:

1. File CA Form 540NR (Nonresident): Report only the income earned during the 3 months in CA. Calculate the tax owed to CA. 
2. File CT-1040 (Resident): Report all your income (CT income + CA internship).
3. Claim the Credit: TurboTax uses the "tax paid" figure from your CA return to fill out Schedule 2 on your CT return. This reduces your CT bill.

Being a "Resident Alien" for federal purposes (passing the Substantial Presence Test) does not automatically make you a CT resident. However if:

1. If you maintained your CT apartment lease for the entire 12 months of 2025 and spent 183+ days there, CT will likely view you as a Statutory Resident. If your lease was only for the school semesters (e.g., you gave up the apartment while in CA), you might not meet the "entire year" requirement for the abode, which would make you a Nonresident.

Recommendation: Most students in your position find it "safer" and simpler to file as a CT Resident and take the credit, as it usually results in the same total tax liability (paying the higher of the two states' rates) while avoiding the risk of the CT DRS auditing your "permanent place of abode" status later.  

[Yujin-Bao]

Thanks very much for your detailed reply and suggestions! It sounds like the safer way is to file as a CT resident in my case.

However, my case might be a little bit different. In 2021, 2022, 2023, and 2024, I did stay in one leased apartment for more than 183 days. But in 2025, I spent the first 5 months in a leased apartment, gave up the lease for my internship in CA, and return to another leased place in CT starting from August. Moreover, if I file as a CT resident, my property tax (car) can generate credit. So while it looks 'easier' to file as a CT resident, I might end up paying less than filing as a CT nonresident (at least this would for sure for 2021, 2022, 2023, and 2024 as I didn't have income from another state). So I wondering if 'ending up paying more tax' by filing as a CT nonresident is actually 'safer' in my case?

[AmyC]

No, the safer option is the accurate one. As an international student, you did have leases over 183 days in CT.  Report all income to CT and claim a credit for the income also taxed by CA. The answers above by @MaryK4   explained well how CT will give you a credit for the CA tax and ends with @DaveF1006  and I agreeing with your original post - CT resident and CA nonresident. In addition, you get to claim the property tax credit on your car.